Title: Interaction of human norovirus with B cells Summary Human noroviruses cause a devastating number of infections that are associated with significant economic losses globally. Thus, there is a critical need for developing effective prevention strategies, therapeutics, and diagnostics platforms for human norovirus infections. However, there is a fundamental gap in understanding the life cycle of human noroviruses at the cellular level due to the historical lack of a cell culture system. The long-term goal of the research program is to increase knowledge of human norovirus biology and to develop effective strategies for their control and prevention. The objective of this application is to develop a robust, easy-to-use, resource-efficient HuNoV culture system and gain critical insights into the fundamental characteristics of infection in B cells. The first description of human norovirus infection in cell culture demonstrated infection of one human norovirus genotype in BJAB human B cells. New data extended these findings to another prevalent genotype, and subcloning of the cell line resulted in clones differentially susceptible to both virus strains. The latter suggested the presence of host factors that promote or inhibit infection. Exciting new data further indicated that the same human noroviruses belonging to two genotypes infected primary human blood-derived B cells in a novel B cell culture system. Addition of the nucleoside analogue 2?-C-methylcytidine blocked infection, confirming viral replication. Infection levels varied by donor and depended on the subtypes of B cells present in the culture. These data led to the central hypothesis that human noroviruses infect specific human B cell subsets and that a host factor(s) restricts virus infection in other subsets. The hypothesis will be tested by pursuing two specific aims: 1) Define parameters of human norovirus infection in primary human B cells; and 2) Determine whether a restriction factor limits human norovirus infection in B cell subsets. The approach is innovative as human norovirus infection will be investigated in two unique human B cell culture models (i.e., BJAB subclones, primary B cells) using a combination of established and newly developed virologic and immunologic tools. The impact of the research is high since it will significantly increase basic knowledge of human norovirus-host interaction and may identify novel targets for the developments for antiviral drugs and immunotherapies. The proposed research is further significant because it is expected to lead to the generation of a human norovirus-susceptible cell line(s) that is easy to use by the entire norovirus research community to address a wide spectrum of basic science and translational research questions. Thus, these studies have the potential to fast-track development of effective vaccines, antivirals and treatment options for human norovirus infections that will ultimately reduce morbidity, mortality and the economic burden associated with human norovirus infections.